Spray Drying Method
Principle of spray drying method
There are many types of drying methods, but the spray drying method is the most widely used one. It refers to atomizing the liquid to be dried into tiny droplets in the drying chamber and let the droplets directly contact and mix with the hot gas of the drying medium to evaporate the water, and then collecting it by gas-solid separation to obtain a powder or granular product. The raw material liquid may be a solution, an emulsion, or a suspension, or maybe a molten liquid or a paste. The drying medium can be air, nitrogen, or superheated steam.
Applications of spray drying method
Spray drying method is very popular among users in pharmaceutical and food industries since spray drying machine can meet the GMP requirements of the two fields and has superior performance. It is especially suitable for the drying and granulation of Chinese and Western medicines and foods. Granules prepared have strong disintegration, good fluidity, and instant solubility, and can be directly used for tableting, capsule filling, granules, and solid drinks.
Spray drying method is also widely used in dye drying. It can dry dye fine powder, super-fine powder, dust-free powder, and hollow granules. This method can be divided into three categories:
(1) airflow atomization, which uses compressed air or water vapor to atomize the material liquid;
(2) pressure atomization, a high-pressure pump is applied to press out the material liquid from the nozzle at high speed and thus forming a mist;
(3) rotary atomization, the material liquid is added to the high-speed rotating disc (7000 ~ 28000r / min) in the atomizer, and then the material liquid is quickly thrown out and atomized. The third category — rotary atomization has a good effect, short time, and high labor productivity, which is favored by the dyestuff industry. But it needs large equipment investment and high energy consumption.
Spray drying method is a representative of systematic technology applied to material drying. After the material is atomized in the drying chamber, the moisture quickly vaporizes in contact with the hot air to obtain the dried product. This method can save the steps of evaporation and crushing. Spray drying method has the characteristics of fast heat-transfer, rapid water evaporation, and short drying time. It can improve the dissolution rate of certain formulations, suitable for heat-sensitive drugs. In addition, spray drying can be used to prepare microcapsules.
Advantages of spray drying method
1. Rapid drying process.
2. Materials can be directly dried into powder.
3. It is easy to change the drying conditions and adjust product quality standards.
4. There is a certain negative pressure in the drying room, which guarantees the hygienic conditions in the production, avoids the dust flying in the workshop, and improves the purity of the product.
5. High production efficiency and fewer operators.
6. Large production capacity and high product quality. The spray volume can reach several hundred tons per hour.
Disadvantages of spray drying method
1. The equipment is complex, covers a large area, and requires a large investment.
2. The price of a spray dryer and powder recovery device is relatively high.
3. The thermal efficiency is not high and the heat consumption is large.